1. Field of the Invention
The present invention relates to the technology fields of image display, and in particular to a polysilicon thin film transistor (TFT) device and the manufacturing method thereof.
2. The Related Arts
Amorphous silicon (a-Si) TFT technology has a simple process and low cost, but the carrier mobility is very small; at the same time, it can only provide N-type amorphous silicon TFT devices and it has problems in the role of stability under long-term stress function. Polysilicon TFT has higher carrier mobility and faster response speed, which is easy to achieve a dynamic video display with large area. Meanwhile, the high carrier mobility can integrate the peripheral driver circuits on the display backplane, which will greatly reduce the external leads and the complexity of the peripheral drive circuit. Currently, the international community generally conducted the AMOLED backplane research and development project using polysilicon TFT.
The channel region of Polysilicon TFT is formed by first forming an amorphous silicon layer on the substrate, and then followed by the recrystallization process on the amorphous silicon layer. The method of recrystallization process includes metal induced crystallization or metal induced lateral crystallization.
Among these methods, metal induced lateral crystallization has better uniformity and cheaper in the TFT device compared to other techniques, which is easier to achieve the requirement of AMOLED display with large size. Meanwhile, the cost of the metal induced lateral crystallization is much cheaper. In addition, as comparing to metal induced crystallization, metal induced lateral crystallization techniques can effectively reduce the residual metal contamination in the channel region.
The main bottleneck in the current AMOLED backplane using metal induced lateral crystallization technology is unable to reduce the leakage current of the TFT. In order to ensure the display of each pixel displaying normally in one frame time, it is necessary to ensure that leakage current will not cause the decreasing voltage value of the storage capacitor more than one gray level when the switching transistor is off. However, because small amount of metal residues is still present in the Polysilicon TFT obtained using metal induced lateral crystallization, the high leakage current of TFT restricts the realization of high-grayscale and high-quality display.